1. Field of the Invention
The present invention relates generally to wireless communication systems, and more particularly, to a scheduling method and an apparatus adapted thereto that can allocate sub-carriers, less susceptible to interference, to a terminal at the cell edge.
2. Description of the Related Art
Orthogonal Frequency Division Multiplexing (OFDM) refers to a method of digital modulation in which a data stream having a high transmission rate is split into a data stream having a low transmission rate, which split data streams are simultaneously transmitted through sub-carriers. In frequency domain, one OFDM symbol is composed of several sub-carriers that are mathematically arranged such that they are orthogonal to each other. Although the sub-carriers are partially superposed in their sidebands, they can be recovered into the original signal at the receiver.
Long Term Evolution (LTE) and WiMAX systems employ OFDMA as multiple access technology.
OFDMA refers to a method of modulation based on a concept in which a plurality of terminals share one physical channel. That is, OFDMA allows respective terminals to simultaneously use a plurality of sub-carriers and to perform multiple access. If a portion of the sub-carriers experience substantial fading, the base station selects only those sub-carriers with favorable channel states and allocates the terminals thereto. If a plurality of terminals exist in a cell, the base station may split sub-carriers in a favorable channel state and then allocate them to respective terminals.
LTE systems and 3.5th to 4th generation mobile communication systems consider the frequency reuse factor of 1. Accordingly, the systems use the total bandwidth to efficiently use frequency resources restricted within all cells or sectors.
However, since adjacent cells use the same frequency band, co-channel interference is a major problem, as it causes deterioration in the link quality of terminals. This co-channel interference is worse in terminals at the cell edge.
In WiMAX and IEEE 802.20 working groups considering mobility, a Fractional Frequency Reuse (FFR) technique has been proposed to resolve a channel problem at the cell edge. The technique, however, is disadvantageous in that it can be performed only when the base station is initially established.
In a Hierarchical Cell Structure (HCS) environment where macro, pico, and femto cells are mixed, small base stations for the pico or femto cell may be arbitrarily established. That is, in such an SCS environment, the conventional FFR technique cannot be effectively employed considering the arbitrarily established base stations.